1. Field of the Invention
The present invention relates to a signal transmission system in a mobile communication network. Specifically, it relates to the signal transmission method between a mobile terminal and a mobile switching center through a base station in a mobile communication network.
2. Description of the Related Art
As to the conventional technologies regarding the connection between a base station and a communication network in a mobile communication system, there is one disclosed in Japanese Patent Application Laid-open No. Hei-6-152601 (hereafter, referred to as Prior Art 1). In Prior Art 1, it is assumed that the connective configuration between base stations 200, 201 and 20n, and a loop-shaped network has been established, as shown in FIG. 15. The Prior Art 1 is configured in such a way that the base station receives signal in a voice packet form sent from a mobile terminal in its own radio zone and the signal is transmitted to a destination mobile terminal via the loop-shaped network. Moreover, according to the approach shown in Prior Art 1, the signal sent from the mobile terminal is supplied in a broadcast signal mode, to the network. Respective radio base stations connected to the network then take in the signal dependent upon the destination address attached to the signal.
As to the description of the conventional signal transmission between a base station and a mobile switching center, there is one titled xe2x80x9cInternational Conference on Universal Personal Communicationxe2x80x9d (ICUPC 95; pp. 863-867; hereafter, referred to as Prior Art 2). In Prior Art 2, the disclosed system is that the signal transmission between the base station (BS) and the mobile switching center (MSC) is performed by the transmission line employing the ATM (Asynchronous Transfer Mode) transmission technology. In addition, according to Prior Art 2, the voice signals output from the mobile terminal are divided into individual cells, and then transmitted, as shown in FIG. 16.
However, the conventional technology of signal transmission between the base station and the mobile switching center in the mobile communication system including the above Prior Arts 1 and 2, is faced with the following problems.
First, in the conventional technologies, when a signal transmission system between the base station and the mobile switching center is the system employing an intermittent transmission approach such a packet transmission, the ATM cell transmission or a frame relay transmission, it may occur discarding of data, or lost of data in a certain condition such as occurrence of congestion along the transmission line. This causes a problem that the original signal cannot be reproduced, or required signal may not be able to arrive by a predetermined time, and maintaining the continuity of signals cannot be guaranteed.
For example, if communication form of the mobile terminal is the voice, the fact that the continuity is not guaranteed indicates that users who are receiving may be able to sense the discontinuity of the voice.
Furthermore, since the voice is quite a real-time signal irrelevant of the bit-rate, even though signals of the discarded data is re-transmitted, the process cannot keep up with the speed.
Moreover, as the methods for correcting an intermittent voice, methods of muting a reproduced voice or repeating the voice frame just before are well-known.
However, neither of the methods can essentially solve the above problems.
Secondly, as long as there is the possibility of data loss or data discarding in the conventional technology and any means to solve the problem is not prepared, it cannot guarantee to maintain the quality of signals transmitted.
Moreover, if the communication form of the mobile terminal is data communication such as a facsimile, which uses multiple data, non-received signal data can be obtained by re-transmission the request of the receiving end. However, the re-transmission results in imposing an excess load on the transmission line. Thereby, another problem occurs wherein limited resources cannot be effectively utilized.
Accordingly, the object of the present invention is to solve the problems with the conventional technologies as described above, and provides a signal transmission system capable of assuring continuity and quality of signals in the mobile communication network even though data packet is lost in the transmission system employing an intermittent transmission approach such as packet transmission, ATM cell transmission or frame relay transmission.
A signal transmission system according to the present invention is for a mobile communication network in which a base station is connected to a mobile switching center through a transmission line and a signal form transmitted between the base station and the mobile switching center is a data packet form. The signal transmission system according to the present invention comprises the following elements.
The base station includes;
a plurality of convolutional encoders, each for convolutionaly encoding digital data from a mobile terminal to signal codes having redundant codes for correction;
a plurality of interleaving units, each for replacing a location of each signal code encoded by the corresponding convolutional encoder; and
a packet generation unit for generating data packets from signal codes output from each of the interleaving units for transmitting to the mobile switching center through the transmission line.
The mobile switching center includes;
a plurality of convolutional code decoders, each for convolutionaly decoding signal codes transmitted from the base station, and reproducing signal codes corresponding to lost packets during transmission, and outputting original digital data for switching.
Above elements are for upward direction signals, therefore, the following elements are also provided for the downward direction signals.
The mobile switching center includes;
a plurality of convolutional encoders, each for convolutionaly encoding digital data output from a switching unit to signal codes having redundant codes for correction;
a plurality of interleaving units, each for replacing a location of each signal code encoded by the corresponding convolutional encoder; and
a packet generation unit for generating data packets from signal codes output from each of the interleaving units for transmitting to the base station through the transmission line.
The base station includes;
a plurality of convolutional code decoders, each for convolutionaly decoding signal codes transmitted from the mobile switching center, and reproducing signal codes corresponding to lost packets during transmission, and outputting original digital data for transmitting to the mobile terminal.
There are several variations of the present invention, and in one of them, the base station further comprises a plurality of punctured code generation units, each for reducing number of signal codes output from corresponding convolutional encoder, and outputting reduced number of signal codes to corresponding interleaving unit, and the mobile switching center further comprising a plurality of punctured code decoders, each for restoring reduced number of signal codes received from the base station to original number of signal codes, and outputting the restored number of signal codes to corresponding convolutional code decoder.
When considering the opposite signal direction, the following variation is also available;
The mobile switching center further comprising a plurality of punctured code generation units, each for reducing number of signal codes output from corresponding convolutional encoder, and outputting reduced number of signal codes to corresponding interleaving unit, and the base station further comprising a plurality of punctured code decoders, each for restoring reduced number of signal codes received from the mobile switching center to original number of signal codes, and outputting the restored number of signal codes to corresponding convolutional code decoder.
Other variation of the present invention is as follows;
a plurality of mobile terminals, each including a convolutional encoder for convolutionaly encoding digital data to signal codes having redundant codes for correction;
the base station includes;
a plurality of interleaving units, each for replacing a location of each signal code received form corresponding mobile terminal; and
a packet generation unit for generating data packets from signal codes output from each of the interleaving units for transmitting to the mobile switching center through the transmission line; and
the mobile switching center includes;
a plurality of convolutional code decoders, each for convolutionaly decoding signal codes transmitted from the base station, and reproducing signal codes corresponding to lost packets during transmission, and outputting original digital data for switching.
Configuration considering the opposite signal direction of the above case is also available.
AS for a method of signal transmission according to the present invention, the method comprises steps of:
in a signal transmission side;
convolutionaly encoding digital data to be transmitted to signal codes having redundant codes for correction;
replacing a location of each signal code having been convolutionaly encoded;
generating data packets, for signal transmission, from signal codes having been replaced each location of convolutionaly encoded signal codes; and
in a signal reception side;
convolutionaly decoding signal codes received from the signal transmission side, and reproducing signal codes corresponding to lost packets during transmission, and outputting original digital data.